Pneumatic radial tire

Abstract: It is intended to improve cut growth resistivity at side portions of a pneumatic radial tire for a construction vehicle without affecting durability. A pneumatic radial tire, particularly for a construction vehicle, has a carcass ply (2) arranged toroidally between a pair of bead cores (1), containing rubber coated steel cords disposed radially therein, being turned up around the bead core from the inside to the outside of the tire and the turn-up portion (3) of which extends to around 1/2 height of the tire height H, characterized in that when the length of an overlapping portion of the turn-up portion (3) of the carcass ply and the main carcass ply (2) is h 1 and the thickness of the overlapping portion is w 1 within a range of ± 0.1 H having half height H/2 of the tire height H as the center, the length h and the thickness w of a reinforcing rubber material (20) arranged between the turn-up portion (3) of the carcass ply and the main ply (2) satisfy the following formulae (1) 0.2w 1 ≦ w ≦ 1.0w 1 , and (2) 0.5h 1 ≦ h ≦ 1.0h 1 , and the reinforcing rubber material (20) satisfies the following conditions (3) 100 parts by weight of rubber is partly comprised by 10-80 parts by weight of a cis-1,4 polybutadiene, and (4) a modulus M is 60kgf/cm 2 ≦ M ≦ 100kgf/cm 2 at 300% elongation and a rebound resilience coefficient R is 0.4 < R < 0.7.

Description: This invention relates to a pneumatic radial tire, particularly for construction vehicles. The invention is concerned with improvement of durability, more particularly improvement of side cut resistivity against external damage of side areas of the tire. In general, since a pneumatic radial tire for a construction vehicle runs on rough roads, side portions can be damaged easily by stones and tree stumps. Side cuts are classified into two groups, firstly leakage of air caused by penetration in the side portion damaged by shock cuts, and secondly leakage of air caused by growing of cuts by repeated deformation resulting in penetration and leakage of air in the side portion. In a pneumatic radial tire for a construction vehicle, conventionally, in addition to extension of turn-up portions of a carcass ply to around the maximum width of the tire, side rubber 6 having good shock cut property or crack growth resistivity may be arranged to extend from buttress portions of a tread to around bead portions covering the outside of a turn-up ply, as shown in Fig. 4(a) of the accompanying drawings, which is a sectional view of a tire of the prior art. Further, at least one reinforcing layer 10 may be arranged outside a main ply, which is damaged by cuts frequently, as shown in Fig. 4(b) of the accompanying drawings, which is a sectional view of another tire of the prior art. It is an object of the present invention to restrain speed of cut growth resulting from leakage of air caused by repeated deformation in a pneumatic radial tire for a construction vehicle without deteriorating other aspects of the tire performance. A tire according to the preamble of claims 1 and 2 is known from US-A-4 086 948. According to a first aspect of the invention, there is provided a pneumatic radial tire, particularly for a construction vehicle, having at least one carcass ply arranged toroidally between a pair of bead cores, containing rubber coated steel cords disposed radially therein, being turned up around the bead core from the inside to the outside of the tire and the turn-up portion of which extends to around one half height H/2 of the tire height H, characterized in that, when the length of an overlapping portion of the turn-up portion of the carcass ply and the main carcass ply is h 1 and the thickness of the overlapping portion is w 1 within a range of ± 0.1 H having half height H/2 of the tire height H as the center, the length h and the thickness w of a reinforcing rubber material arranged between the turn-up portion of the carcass ply and the main ply satisfy the following formulae (1) 0.2w 1 ≤ w ≤ 1.0w 1 , and (2) 0.5h 1 ≤ h ≤ 1.0h 1 , and the reinforcing rubber material satisfies the following conditions (3) 100 parts by weight of rubber is partly comprised by 10-80 parts by weight of a cis-1,4 polybutadiene, and (4) a modulus M is 60kgf/cm 2 ≤ M ≤ 100kgf/cm 2 at 300% elongation and a rebound resilience coefficient R is 0.4 < R < 0.7. In the condition (4), by modulus M at 300% elongation, there is meant that the modulus is measured when the rubber is stretched 300%, that is the rubber is stretched to four times its original length. According to a second aspect of the invention, there is provided a pneumatic radial tire, particularly for a construction vehicle, having at least one carcass ply arranged toroidally between a pair of bead cores, containing rubber coated steel cords disposed radially therein and being turned up around the bead core from the inside to the outside of the tire, and at least one independent reinforcing layer containing rubber coated reinforcing cords therein in a side portion of the tire, characterized in that, when the total length of the length of an overlapping portion of the reinforcing layer and a main carcass ply and the length of an overlapping portion of a turn-up portion of the carcass ply and the main carcass ply is h 2 , and the thickness of the overlapping portion of the reinforcing layer and the main ply is w 2 within a range of ± 0.1 H having half height H/2 of the tire height H as the center, the length h and the thickness w of a reinforcing rubber material arranged between the reinforcing layer and the main ply satisfy the following formulae (1) 0.2w 2 ≤ w ≤ 1.0w 2 , and (2) 0.5h 2 ≤ h ≤ 1.0h 2 , and the reinforcing rubber material satisfies the following conditions (3) 100 parts by weight of rubber is partly comprised by 10-80 parts by weight of a cis-1,4 polybutadiene, and (4) a modulus M is 60kgf/cm 2 ≤ M ≤ 100kgf/cm 2 at 300% elongation and a rebound resilience coefficient R is 0.4 < R < 0.7. When a pneumatic radial tire for a construction vehicle is deformed by applying a load, since portions around one half height H/2 of the tire height H expand outward of the tire, which is easily damaged by cuts by stones and tree stumps, and since the portions have a strong circumferential tension at the surface of the tire, these portions are liable to suffer cut damage. For this reason, in a pneumatic radial tire for a construction vehicle, a turn-up portion of a carcass ply extends to around one half height H/2 of the tire height H in order to obtain durability of the carcass ply. As a result, the turn-up portion of the carcass ply prevents cuts by stones or the like from growing deeper, and penetration in the side portions of the tire decreases drastically. However, leakage of air caused by cut growth continues long after the tire has suffered the cuts. Thus, it becomes important to restrain the cut growth. In a pneumatic radial tire for a construction vehicle, the cuts which stop at the turn-up portion of the carcass ply grow inside the tire because of convergence of stress into the cuts, by the circumferential strain during running and the shearing strain between the turn-up portion of the carcass ply and the main ply. Consequently, it is necessary to restrain the cut growth inside the turn-up portion of the carcass ply around one half height H/2 of the tire height H. The present inventors have found that, when the overlapping length of an overlapping portion of a turn-up portion of a carcass ply and a main carcass ply is h 1 and the thickness of the overlapping portion is w 1 within a range of ± 0.1 H having half height H/2 of the tire height H as the center, the length h and the thickness w of a reinforcing rubber material arranged between the turn-up portion of the carcass ply and the main ply satisfy the following formulae (1) 0.2w 1 ≤ w ≤ 1.0w 1 , and (2) 0.5h 1 ≤ h ≤ 1.0h 1, and the reinforcing rubber material satisfies the following conditions (3) 100 parts by weight of rubber is partly comprised by 10-80 parts by weight of a cis-1,4 polybutadiene, and (4) a modulus M is 60kgf/cm 2 ≤ M ≤ 100kgf/cm 2 at 300% elongation and a rebound resilience coefficient R is 0.4 < R < 0.7, are effective. The reinforcing rubber material includes high cis-1,4 polybutadiene for anti-crack growth purposes. If the content of cis-1,4 polybutadiene is less than 10 parts by weight, recommended crack growth resistivity cannot be obtained; while if the content of cis-1,4 polybutadiene exceeds 80 parts by weight, breaking strength property deteriorates. If the modulus M is less than 60kgf/cm 2 , rigidity of the tire deteriorates; while if the modulus exceeds 100 kgf/cm 2 , the crack growth resistivity decreases and rigidity of the tire deteriorates. If the rebound resilience coefficient is equal to or less than 0.4, durability of the tire deteriorates; while if the rebound resilience coefficient is equal to or greater than 0.7, the crack growth resistivity cannot be obtained. If the thickness w of the rubber material is less than 0.2 of w 1 , crack growth cannot be restricted; while if w exceeds 1.0w 1 , the weight of the tire increases too much. If the length h of the rubber material is less than 0.5h 1 , the crack growth cannot be restricted; while if the length h is greater than 1.0h 1 , the weight of the tire increases too much. According to the second aspect of the invention, in a pneumatic radial tire for a construction vehicle having a carcass ply arranged toroidally between a pair of bead cores, containing rubber coated steel cords disposed radially therein and being turned up around the bead core from the inside to the outside of the tire, and at least one independent reinforcing layer containing rubber coated reinforcing cords therein in a side portion of the tire, the reinforcing rubber material having above mentioned conditions is also effective. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a sectional view of a tire of a first embodiment of the present invention; Figs. 2(a) and 2(b) are sectional views of tires of second and third embodiments of the present invention; Fig. 3 is a sectional view of a tire of a fourth embodiment of the present invention; and Figs. 4(a) and 4(b) are sectional views of tires of the prior art. A pneumatic radial tire for a construction vehicle having a size of 18.00R33 was used as an embodiment of the present invention. The pneumatic radial tire of a first embodiment shown in Fig. 1 has a carcass 2 comprising steel cords disposed toroidally and radially between a pair of bead cores 1, the carcass being turned up around the respective bead cores from the inside to the outside of the tire to form turn-up portions 3 of the carcass. The carcass has steel cords whose construction is 1 x 3 + 9 + 15 with a stretch strength of 300kgf/piece. A belt layer 4 comprising four steel cord layers intersecting each other is arranged radially outside of the carcass 2, and a tread 5 is arranged radially outside of the belt layer. The belt layer 4 consists of two intersecting layers having steel cords whose construction is (1 + 6) + 6 x (1 + 6) with a stretch strength of 400 kgf/piece and two intersecting layers having high elongation cords whose construction is 3 x 7 with a stretch strength of 170 kgf/piece. Each layer intersects each other layer at an angle of 23° with respect to an equatorial plane of the tire. A sidewall rubber 6 is arranged radially outside of a turn-up portion 3 of the turn-up carcass ply 2. The carcass ply is turned up around the bead core 1 and extends to around one half height H/2 of the tire height H. A stiffener rubber 7 is arranged radially outside the bead core 1, and a pad rubber 8 is arranged along the carcass ply 2 between the stiffener rubber 7 and the turn-up portion 3 of the carcass ply. In the first embodiment, a reinforcing rubber material 20 having a length h of 0.7h 1 and a thickness w of 1.0w 1 within a range of ± 0.1 H having half height H/2 of the tire height H as the center is positioned between the turn-up portion 3 of the carcass ply and the main ply 2, where h 1 is the length of an overlapping portion of the turn-up portion of the carcass ply 3 and the main ply 2, and w 1 is the thickness of the overlapping portion. In a second embodiment of the invention as shown in Fig. 2(a), a reinforcing rubber material 20 having a length h of 0.9h 1 and a thickness w of 0.3w 1 within a range of ± 0.1 H having half height H/2 of the tire height H as the center is positioned between the turn-up portion of the carcass ply and the main ply. In a third embodiment of the invention as shown in Fig. 2(b), the construction is almost the same as that of the first and the second embodiments, but the pad rubber 8 functions as the reinforcing rubber material 20 at the same time. The reinforcing rubber material 20 having a length of 1.0h 1 and a thickness w of 1.0w 1 within a range of ± 0.1 H having half height H/2 of the tire height H as the center is positioned between the turn-up portion of the carcass ply and the main ply. In a fourth embodiment of the invention as shown in Fig. 3, which is similar to the conventional tire shown in Fig. 4(b), in a tire having a reinforcing cord layer 10 independent from the turn-up portion of the carcass ply, the reinforcing rubber material 20 having a length h of 1.0h 2 and a thickness w of 1.0w 2 is positioned between the turn-up portion of the carcass ply and the main ply. In the fourth embodiment of the invention, the total length of the length of an overlapping portion of the reinforcing layer and a main carcass ply 2 and the length of an overlapping portion of a turn-up portion 3 of the carcass ply and the main carcass ply is h 2 , and the thickness of the overlapping portion of the reinforcing layer 10 and the main carcass ply 2 is w 2 within a range of ± 0.1 H having half height H/2 of the tire height H as the center. It should be noted that, in the embodiment shown in Fig. 3, the turn-up portion 3 of the carcass ply does not overlap with the main ply 2 within the range of ± 0.1 H. The composition of the reinforcing rubber material of the first, second, third and fourth embodiments is shown in Table 1. The same composition is used for all four embodiments. In the reinforcing rubber material, a modulus M is 75kgf/cm 2 at 300% elongation and a rebound resilience coefficient R is 0.6. Composition of the reinforcing rubber material (Parts by weight) Natural rubber 50 High cis-1,4 polybutadiene 50 Carbon black (HAF) 40 Sulfur 1.5 Zinc white 3 Vulcanization accelerator (NS) 1 Stearic acid 2 Age resister 2 In order to evaluate the effects of the first (Fig. 1), second (Fig. 2(a)) and third (Fig. 2(b)) embodiments, a prior art tire 1 (Fig. 4(a)) was prepared as a comparison; and in order to evaluate the fourth embodiment (Fig. 3), a prior art tire 2 (Fig. 4(b)) was prepared. Cut growth resistivity and durability were tested under the following conditions. In order to evaluate the cut growth resistivity, cuts having a length of 80mm, a width of 0.5mm, a depth reaching the turn-up portion of the carcass ply and angles (of the cuts) of 0° and 15° with respect to the radial direction of the tire were formed previously, and the tires were run on a drum. Running time until leakage of air occurred was indexed for evaluation purposes. In the drum test, the air pressure was 7.0 kPa, the speed was 10.0km/h, the load was 11.0 ton and the diameter was 4000mm. The results are shown in Table 2 below. In the Table, the results of the first, second and third embodiments are expressed using an index that the running time of the prior art tire 1 is 100, and the result of the fourth embodiment is expressed using an index that the running time of the prior art tire 2 is 100. In the Table, the higher the value, the better the performance. As is apparent from the Table, the cut growth resistivity of the tire of the first embodiment is 150, that of the second embodiment is 130, and that of the third embodiment is 160; thus, remarkable cut growth resistivity can be observed compared with the prior art tire 1. In the tire of the fourth embodiment, remarkable cut growth resistivity can also be observed compared with the prior art tire 2. In order to evaluate durability, running time of a tire without forming cuts, which runs on a drum, until damage occurs was indexed for evaluation purposes . In the Table, the results of the first, second and third embodiments are expressed using an index that the durability of the prior art tire 1 is 100, and the result of the fourth embodiment is expressed using an index that the durability of the prior art tire 2 is 100. In the Table, the higher the value, the better the performance. As is apparent from the Table, the tires of the first, second and third embodiments have almost the same durability as the prior art tire 1, and also the tire of the fourth embodiment has the same durability as the prior art tire 2. Embodiment 1 Embodiment 2 Embodiment 3 Prior Art 1 Embodiment 4 Prior Art 2 Cut Growth Resistivity 150 130 160 100 150 100 Durability 100 100 98 100 100 100 As can be seen from the above explanation, a pneumatic radial tire for a construction vehicle according to the first aspect of the invention improves cut growth resistivity remarkably without affecting durability compared with a conventional tire. Further, a pneumatic radial tire for a construction vehicle according to the second aspect of the invention also improves cut growth resistivity without affecting durability compared with the conventional tire.

Claims: A pneumatic radial tire, having at least one carcass ply (2) arranged toroidally between a pair of bead cores (1), containing rubber coated steel cords disposed radially therein, being turned up around the bead core from the inside to the outside of the tire and the turn-up portion (3) of which extends to around one half height H/2 of the tire height H, characterized in that, when the length of an overlapping portion of the turn-up portion (3) of the carcass ply and the main carcass ply (2) is h 1 and the thickness of the overlapping potion is w 1 within a range of ± 0.1 H having half height H/2 of the tire height H as the center, the length h and the thickness w of a reinforcing rubber material (20) arranged between the turn-up portion (3) of the carcass ply and the main ply (2) satisfy the following formulae (1) 0.2w 1 ≤ w ≤ 1.0w 1 , and (2) 0.5h 1 ≤ h ≤ 1.0h 1 , and the reinforcing rubber material (20) satisfies the following conditions (3) 100 parts by weight of rubber is partly comprised by 10-80 parts by weight of a cis-1,4 polybutadiene, and (4) a modulus M is 60kgf/cm 2 ≤ M ≤ 100kgf/cm 2 at 300% elongation and a rebound resilience coefficient R is 0.4 < R < 0.7. A pneumatic radial tire, having at least one carcass ply (2) arranged toroidally between a pair of bead cores (1), containing rubber coated steel cords disposed radially therein and being turned up around the bead core from the inside to the outside of the tire, and at least one independent reinforcing layer (10) containing rubber coated reinforcing cords therein in a side portion of the tire, characterized in that, when the total length of the length of an overlapping portion of the reinforcing layer (10) and a main carcass ply (2) and the length of an overlapping portion of a turn-up portion (3) of the carcass ply and the main carcass ply is h 2 , and the thickness of the overlapping portion of the reinforcing layer (10) and the main carcass ply (2) is w 2 within a range of ± 0.1 H having half height H/2 of the tire height H as the center, the length h and the thickness w of a reinforcing rubber material (20) arranged between the reinforcing layer (10) and the main ply (2) satisfy the following formulae. (1) 0.2w 2 ≤ w ≤ 1.0w 2 , and (2) 0.5h 2 ≤ h ≤ 1.0h 2 , and the reinforcing rubber material (20) satisfies the following conditions (3) 100 parts by weight of rubber is partly comprised by 10-80 parts by weight of a cis-1,4 polybutadiene, and (4) a modulus M is 60kgf/cm 2 ≤ M ≤ 100 kgf/cm 2 at 300% elongation and a rebound resilience coefficient R is 0.4 < R < 0.7.

Inventors: FUKUSHIMA MASAHARU, NAGAI YUICHI, FUKUSHIMA, MASAHARU, NAGAI, YUICHI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1994
Main classification: B60C13
IPC codes: B60C15, B60C13